The present invention concerns a life predicting method for a rolling bearing, a life predicting device, a rolling bearing selecting device using the life predicting device, a program therefor and an environment coefficient determining method.
A basic rated life L10 of a rolling bearing is defined in JIS B 1518: 1992 and, usually, a calculation formula as shown in the following formula (1) is used.L10=(C/P)p  (1)in which C represents a basic dynamic rated load of a rolling bearing and P represents a dynamic equivalent load exerting on the bearing. Further, p represents a load index which is set at p=3 in the case of a ball bearing and p=10/3 in the case of a roller bearing. The basic rated life L10 is defined for a case at a reliability of 90%, using a material used generally, for usual manufacturing quality and under usual working conditions.
It is noted that in the calculation formula for the basic rated life, only the effect of the bearing load on the bearing life is taken into consideration. In view of the above, the result of the calculation formula for the basic rated life is greatly different from the result of life in the market at present. This is because the fatigue life has also been improved by the improvement in the bearing steel materials, and the effect of the lubricant film thickness at the contact portion between a bearing ring and a rolling element on the fatigue life has been analyzed by a study on the theory of elastic fluid lubrication in recent years. A correction rated life Lnm reflecting the effect of them on the life calculation formula was proposed as the following formula (2) by using a life correction coefficient axyz by ISO 281 in February, 2000.Lnm=a1·axyz·L10  (2)
Further, the life correction coefficient axyz is shown by the following equation (3).axyz=f(Pu,κ,ac)  (3)
The life correction coefficient axyz is represented as a function considering factors such as fatigue limit load Pu, lubrication state (kinetic viscosity) κ, and environment coefficient (contamination degree of lubricant) ac. Further, a1 is a reliability coefficient which is described in the following Table 1 and it takes a lower value as the reliability is improved.
TABLE 1Reliability %Lnaa190L10a195L5a0.6296L4a0.5397L3a0.4498L2a0.3399L1a0.21
However, among the variables representing the life correction coefficient axyz, the fatigue limit load Pu and the lubrication state (kinetic viscosity) κ are considered quantifiable. However, while the weight, size, shape and substance of foreign substance are considered for the contamination degree ac of the lubricant, they are not quantitatively evaluated but merely represent the environment ambiguously. This has resulted in a problem that the life can not be predicted at high accuracy according to the formula (2).
The present invention has been achieved taking into consideration factors of the prior art which had not theretofore been apparent and it is an object thereof to provide a life predicting method for a rolling bearing capable of predicting the life at a high accuracy according to the formula (2) for calculating a correction rated life, a life predicting device, a rolling bearing selecting device using the life predicting device, a program therefor and an environment coefficient determining method.